1. Field of the Invention
The invention relates to a new class of membrane, for use in protective clothing and to methods of making such membranes. More specifically, the present invention relates to a polymer-polymer membrane with an ionic polymer within the nanopores of a porous polymer host membrane and to methods for making such membranes.
2. Description of the Related Technology
Chemical protective clothing (CPC), which is manufactured for purposes, such as the cleanup of chemical spills, was suggested for applications in homeland defense (Arca et al., 1999). The materials used in these suits (e.g., Tychem® (DuPont), Tyvek® (DuPont), Barricade® (Dupont), 4H® (Safety 4, Inc.), Chemrel® (Chemron UK), Nomex® (Dupont), Responder® (Life-Guard), Saranex® (Dow), Trellchem® (Trelleborg Protective Products AB)) provide good barrier properties for most chemicals. However, they are also good barriers for water vapor (i.e., perspiration), and therefore, are usually referred to as first-responder suits when applied to homeland defense applications since their water-permeability characteristics make them impractical for extended use or wear periods.
Butyl rubber has also been used for protective clothing and may still be found in gloves and boots. Butyl rubber is an effective barrier to most harmful agents at certain thicknesses. However, similar to CPC, butyl rubber is also a barrier to water vapor. Wearing garments manufactured from this material in combat or other situations that involved physical activity is not practical, since the lack of breathability causes tremendous heat fatigue and exhaustion.
A more recent approach taken by the military has focused on using protective suits, such as MOPP (Military Oriented Protective Posture) and JSLIST (Joint Service Lightweight Integrated Suit Technology), which use sorption materials to absorb chemical/biological agents. More specifically, this technology is based on absorbing harmful agents with activated carbon fillers. JSLIST is more breathable than butyl rubber, but does not provide as much protection from chemical/biological agents and is still heavy and bulky, which limits working in these suits to about 45 minutes per hour. In addition, suits based on this sorption principle have a limited overall lifetime.
A variety of selective polymer membranes have also been proposed for this application. Exemplary patents are U.S. Pat. No. 5,024,594 (Athayde et al.); U.S. Pat. No. 4,943,475 (Baker et al.); U.S. Pat. No. 5,743,775 (Baurmeister); U.S. Pat. No. 4,039,440 (Cadotte); U.S. Pat. No. 4,194,041 (Gore et al.); U.S. Pat. No. 4,518,650 (Grot et al.); U.S. Pat. No. 4,469,744 (Grot et al.); U.S. Pat. No. 6,187,696 (Lim et al.); U.S. Pat. No. 6,395,383 (Maples); U.S. Pat. No. 5,260,360 (Mrozinski et al.); U.S. Pat. No. 4,515,761 (Plotzker); U.S. Pat. No. 5,740,551 (Walker); U.S. Pat. No. 5,824,405 (White); and U.S. Pat. No. 5,391,426 (Wu). However, no single technology has emerged that satisfies the necessary technical requirements of being chemically selective, flexible, durable, water-permeable and cost-effective.
U.S. Pat. Nos. 5,928,804 and 6,375,885 describe the sorption of Nafion® onto collinear cylindrical pores of neutron track etched polycarbonate (PC) membranes.
U.S. Pat. No. 6,402,958 describes composite membranes with an ion-conducting polymer embedded within a porous substrate. The porous substrate comprises randomly oriented fibers. Ion-conducting polymers include Nafion® (perfluorosulfonic acid polymers), styrene-(ethylenebutylene)-styrene as well as other styrene components that may be functionalized with sulphonate, phosphoric or phosphonic groups.
U.S. Pat. No. 6,689,501 describes a composite membrane comprising a porous polymeric substrate such as expanded polytetrafluorethylene and an impregnant comprising an ion exchange material. The impregnant may include perfluorosulfonic acid polymers (e.g. Nafion®) or fluorostyrenic polymers such as alpha-fluorostyrene.
Preferably, chemical/biological protective clothing for everyday use should be protective, breathable (i.e. water-permeable), lightweight, flexible, durable, robust, launderable, cost-effective, and processable (i.e., easily integrated with a fabric/textiles)
Accordingly, there is a need in the art for improved materials for use in protective clothing. There is also a need in the art for suitable methods for fabricating improved protective clothing.